Retardation effect of trimethyl phosphite on chelate ring closure of 2,2′-bipyridine (bipy) in cis-[W(CO)4{P(OMe)3}(bipy)]

Abstract

In order to study the effect of a donor ligand on the chelate ring-closure reaction of a diimine ligand co-ordinated in monodentate fashion, cis-[W(CO)₄{P(OMe)₃}(bipy)] was synthesised from [W(CO)₅{P(OMe)₃}] and 2,2′-bipyridine (bipy) by using a newly developed method and characterized by means of IR and NMR spectroscopies. The complex was found to undergo neither cis→trans isomerization nor chelation thermally up to 150 °C. However the ring-closure reaction occurs photochemically. Thus irradiation of the complex yielded fac-[W(CO)₃{P(OMe)₃}(bipy)] which was also isolated and characterized. The extraordinary retardation effect of trimethyl phosphite on the ring-closure reaction of the 2,2′-bipyridine ligand is attributed to the reduction in substitution lability of the CO groups in the complex upon introduction of the phosphite donor ligand.